1. Field of the Invention
The present invention relates to a method of and apparatus for printing a photograph and more particularly, to a photograph printing method and apparatus in which a film image is printed on photographic by automatically determining a printing light quantity on the basis of film image density.
2. Description of the Related Art
The light of three colors, i.e., blue (B), green (G) and red (R), transmits a color negative film. It is a known rule of thumb that transmitting ratios of these three color components are typically equal or constant. For this reason, in an automatic printer a printing light quantity (an exposure quantity) is determined in accordance with the following formula. EQU logFj=Kj+Dj (1)
where logF is the logarithm of the printing light quantity, K is the constant, D is the image density of the negative film, e.g., typically a Large Area Transmittance Density (LATD), measured by a photometer system and j is any one of the color beams B, G and R.
When controlling the printing light quantity by the automatic printer in accordance with the formula (1), however the following defects are caused. A print from a overexposure negative film when photographing a gray subject exhibits a higher density on the whole than a print from a properly exposed negative film. Whereas in a print from an overexposed negative film, the density decreases. Hence, the exposure quantity is determined by correcting Dj of the formula (1) under slope control. On the other hand, even in an automatic printer incorporating a slope control function, an ill-color-blanched defective print tends to be produced from a negative (a heterogeneous light source negative) obtained by photographing with a light source (a fluorescent lamp, a tungsten lamp or the like) remarkably different from the day light or from a color failure negative. For this reason, the exposure quantity is determined by further correcting Dj (color correction) of the formula (1). In this case, an excessive correction with respect to a standard correction (normal correction) is referred to as a high correction, while an extremely small correction is referred to as a lower correction.
In addition to a normal negative (a negative film requiring 3-9 months from film manufacturing to photographing and 1-2 weeks from photographing to film developing), however, there are negatives substantially varied with a passage of time. FIG. 3 shows variations .DELTA.D in print density versus elapsed days (unit is a year: the numeral 1 represents 365 days, and 2 indicates 730 days) from film manufacturing with respect to a certain printing light quantity. Film characteristics change with a passage of time, i.e., with an elapse of days. The variations .DELTA.D in the print density thereby become large. Hence, a degree of the color correction has hitherto been determined on the average of the normal negative and the negative remarkably changed with a passage of time. Therefore, the degree of correction becomes increased for the normal negative, whereby color and density failures tend to take place. Whereas for the negative, substantially varied with an elapse of time, the degree of correction decreases. The problem is that it is difficult to determine an optimum printing light quantity for all the negatives.
The following is an explanation of one known printing method. When manufacturing a film, a reference density is printed on a portion other than a photographic region of the film. The reference density is read during printing to judge the characteristics of the film. Based on this judgment, printing is effected. During a period from film manufacturing to its developing, however, a retrograde of a latent image proceeds. This results in such a problem that the film characteristics can not be obtained with a high degree of accuracy. The reference density and information on the light source are printed during photographing. The density and information are read during printing, thereby judging the film characteristics (Japanese Patent Application Laid-Open Nos. 51-117632, 52-13333 and 59-214023). However, the film characteristics can not, as in the previous case, be accurately obtained because of the retrograde of the latent image from photographing to film developing.